This question is regarding the applicability of a process water re-use and treatment system for WE credits 1.1-3.2. Our coastal project is proposing the use of a ground-coupled open-loop heat rejection system with a side-stream desalination plant. The system draws non-potable brackish water from the ground, rejects heat from cogeneration and HVAC systems into the water and returns the rejected process water to the ground. The water is not potable source water (e.g. sourced from potable watersheds such as lakes and rivers) and stringent environmental regulations are in place with regard to pumping rates / volume, and quality of the return water. Approximately 10% of the rejected process water flow is diverted for re-use in the building. The diverted water is treated using a reverse osmosis desalination system. The treated water will be used onsite for irrigation and conveyance. Benefits of this system include a reduced impact on the already taxed local potable water supply, reliability of water source, and environmental benefit due to on site treatment and re-use. We believe we should be able to take credit for the municipal water savings resulting from this system, provided that energy use from the system is included in energy calculations. Please provide guidance for credit applicability.
The applicant is inquiring as to acceptability of a process water re-use and treatment system for WE credits. In previous CIRs, recycled on-site water (such as water from a cooling tower) has been accepted for credit compliance. However, in this case, the portion of brackish water not returning to the ground from the ground-coupled open loop rejection system, which would be diverted for re-use on site, can not be used as is. Before this water could be put to any use, it would require going through Reverse Osmosis (RO) treatment which is an energy intensive process. The applicant is correct in suggesting that using this water would reduce/eliminate the need to use municipal potable water for landscape irrigation. In order to take credit for using non-potable water the energy use to desalinate the water must also be included in the EAc1 calculations. In addition, it should be noted that the intent of this credit is to encourage water efficient or xeriscape landscaping practices, which require little to no irrigation and/or use no potable water for irrigation. Hence, the project team should be ready to document the overall approach towards meeting the intent of the credit. Applicable Internationally.